Yi-Ci Gao

Syntheses, characterization and crystal structure of copper(II) α,β-unsaturated carboxylate complexes with imidazole

Abstract Four copper(II) α,β-unsaturated carboxylate complexes with imidazole, Cu(CH2=CH–COO)2(imH)2 (1), Cu2(CH2=CH–COO)4(imH)2 (2), Cu[CH2=C(CH3)–COO]2(imH)2 (3) and Cu2[CH2=C(CH3)–COO]4(imH)2 (4) (where imH=imidazole) have been prepared and characterized by elemental analyses, IR, ESR and electronic reflectance spectroscopies. The single crystal X-ray diffraction study of complex 3 shows that the copper(II) atom is in a symmetric centre of a square planar environment completed by two monodentate α-methacrylate groups and two imidazole ligands displayed in trans position. Each molecular unit is linked with four neighbouring units by hydrogen-bond interactions forming a two-dimensional supramolecular compound (dN⋯O=2.781 A). Complex 1 has a similar structure as complex 3, while complexes 2 and 4 have a binuclear cage structure. The ESR spectra show that the spin coupling between the unpaired electrons of Cu(II) atoms present in complexes 2 and 4, is not observed in complexes 1 and 3. The electronic reflectance spectra suggest that the d–d transitions of complexes 1 and 3 are in a square planar ligand field, while that of complexes 2 and 4 are in a tetragonal ligand field, and the ligand field strength of acrylate group and α-methacrylate group is similar. Complexes 1 and 2 as well as 3 and 4, were produced simultaneously in the reaction of the corresponding copper(II) α,β-unsaturated carboxylate with imidazole in methanol solution.

Kinetic studies of CO substitution of metal carbonyls in the presence of O-atom transfer reagents

Abstract Kinetic studies of CO substitution of metal carbonyls in the presence of O-atom transfer reagents show the reaction rates are first-order in metal carbonyl and in O-atom transfer reagent concentrations, but zero-order in entering-ligand concentration. This suggests an associative mechanism where a carbonyl C-atom is attacked by the O-atom of the reagent, affording the good leaving group CO2 and generating an active intermediate which readily reacts with the entering ligand to produce the monosubstituted product. Metal carbonyls that have been investigated include the mononuclear compounds M(CO)6 (M = Cr, Mo, W), M(CO)5L, and M(CO)5 (M = Fe, Ru, Os) as well as the cluster compounds (M3(CO)12 (M = Fe, Ru, Os), M2(CO)10 (M = Mn, Re), M3(CO)11 L (M = Fe, Ru, Os), and M4(CO)12 (M = Co, Ir). Most of the studies involve reactions with (CH3)3 NO, but other O-atom transfer reagents studied include C6H5IO, other amine oxides, pyridine oxides, (p-CH3OC6H4)2EO (E = Se, Te), (C6H5)3EO (E = P, As, Sb), and (C6H5)SO. Various factors relating to the metal carbonyls and to the O-atom transfer reagents that effect the rates of CO substitution are discussed.

Synthesis, Crystal Structure, and Properties of Novel Five‐Coordinate Complexes of Zinc(II) and Copper(II) with tris(2‐Benzimidazolylmethyl)amine

Abstract Two complexes of zinc(II) and copper(II) with tris(2‐benzimidazolylmethyl)amine (ntb) and the anion of acrylic acid of the compositions [M(ntb)(acrylate)](acrylate) · 2.5H2O (M = Zn or Cu) were synthesized and characterized by means of elemental analyses, thermal analyses, IR and H1 NMR spectra. The crystal structure of the novel compound [Zn(ntb)(acrylate)](acrylate) · 1.63H2O has been determined by a single‐crystal x‐ray diffraction method and shows that each zinc ion is linked to tris(2‐benzimidazolylmethyl)amine (ntb) and an acrylate; but another acrylate is the anion of the complex. The zinc ion is five‐coordinate with a N4O ligand set. The coordination geometries of the zinc ion maybe best described as a distorted trigonal‐bipyramid of site symmetry C3.

Molecular structure, characterization and magnetic properties of novel mixed-valence copper(I,II) alpha,beta-unsaturated carboxylate complexes with triphenylphosphine and methanol ligands

Two new mixed-valence tetranuclear copper(I,II) ol,a-unsaturated carboxylate complexes Cu(2)(I)Cu(2)(II)A(6)(PPh3)(4)( CH3OH)(2) (1, A = CH2=CH-COO-; 2, A = CH2=C(CH3)-COO- ) have been synthesized by partial reduction of Cu(2)A(4)(H2O)(2) by triphenylphosphine in methanol solution, and characterized by elemental analyses, IR, ESR, electronic reflectance spectroscopies as well as magnetic susceptibility measurements. In complex 2 two copper(II) atoms in a molecule are linked by four carboxylate groups forming a dimeric unit Cu(2)(II)A(4), and each copper(II) atom coordinates with a copper(I) moiety through a mu(2)-O,O carboxylate group. The electronic reflectance spectra in the solid state suggest a square pyramidal coordination environment around the copper(II) atoms. Bond valence calculations further confirm the presence of the mixed-valence system and the oxidation state of the copper atoms. Room temperature X-band ESR spectra of powdered samples and variable-temperature magnetic susceptibility studies indicate the presence of strong antiferromagnetic exchange interactions between two copper(II) atoms, with 2J= - 310 cm(-1) for complex 1 and 2J= - 288 cm(-1) for-complex 2. The formation mechanism of the title complexes and the structural interconversion among related mixed-valence copper(I,II) carboxylate complexes are also discussed

Kinetics and mechamisms of CO substitution of M4(CO)11L(M = Co, Ir; L = PPh3 PnBu3, P(OMe)3, P(OEt)3) with L in the presence of the Me3NO

Abstract Reported are rates of CO substitution by L of M 4 (CO) 11 L(M = Co, Ir; L = PPh 3 , P n Bu 3 , P(OMe) 3 , P(OEt) 3 ) in the presence of added Me 3 NO. The rate law is the same as that found earlier on such reactions, being first-order in the concentrations of metal carbonyl and of Me 3 NO but zero-order in ligand concentration. The Ir compounds react from 2 to 7 times faster than do the corresponding Co compounds, and for each the rates of reaction with changes in ligand decrease in the order P(OMe) 3 > P(OEt) 3 > P n Bu 3 . The results are compared with earlier studies in the M 3 (CO) 12 and M 3 (CO) 11 L (M = Fe, Ru, Os) clusters, where it was found that the reactivities decrease in the order Fe > Ru > Os. That this order differs from that now reported (Co 4 (CO) 11 L clusters is discussed in terms of the presumed important contribution of CO bridging to the rates of associative reactions in metal carbonyl clusters.

Synthesis, crystal structure and characterization of ternary complexes of lanthanide(III) 3,5-di-tert-butyl-γ-resorcylate with substituted pyridine-N-oxide

Twenty one ternary complexes of lanthanide with 3,5-di-tert-butyl-gamma-resorcylic acid (L) and seven different substituted pyridine-N-oxides (L1-7), with compositions of REL3L21-7. nH(2)O (RE=Nd, Gd, Er; L-1=4-picoline-N-oxide; L-2=4-phenyl-pyridine-N-oxide; L-3=pyridine-N-Oxide; L-4=3-picoline-N-oxide; L-5 =quinoline-N-oxide; L-6=iso-quinoline-N-oxide; L-7=4-methoxyl-pyridine-N-oxide; n=0, 1, 2, 5), were synthesized and characterized by means of elemental analysis, electrical conductivity, thermal analysis and IR spectra. The novel crystal structure of ErL3L23.(EtOH) has been determined by a single-crystal X-ray diffraction method. It shows that each erbium ion is linked to three 3,5-di-tert-butyl-gamma-resorcylic acid ions through two different types of dentation modes in which only the carboxylate oxygen atoms participate. The coordination geometries of erbium ion can be described as a distorted octa-coordinated bicapped trigonal prism

Synthesis and crystal structure of the complex [Lu(bzimpy-H)(NO3)2(CH3OH)2] · bzimpy · 2CH3OH

Abstract The reaction of the ligand 2,6-bis(benzimidazol-2-yl) pyridine (bzimpy) with Lu(NO33 · 6H2O led to the formation of the title complex [Lu(bzimpy-H) (NO32(CH3OH2] · bzimpy · 2CH3OH, in which bzimpy-H is the mono anion derived by deprotonation of bzimpy. The lutetium atom is nne coordinate, and has one tridentate bzimpy-H anionic ligand, two bidentate NO3 groups, and two CH3OH molecules, bonded in a distorted tricapped trigonal prismatic geometry.

Syntheses, characterization, crystal structure and magnetic properties of copper(II) α,β-unsaturated carboxylate complexes with trimethyl phosphate

Two ternary complexes Cu2A4[OP(OCH3)3]2 (A represents CH2=CH-COO− and CH2= C(CH3)-COO− have been synthesized, and elemental analyses, IR, ESR, electronic reflectance spectra and magnetic studies were carried out. The single crystal X-ray diffraction shows that Cu2[CH2=C(CH3)-COO]4[OP(OCH3)3]2 is triclinic, with space group P1, a = 1.05128(13), b = 1.7559(5), c = 1.94479(3) nm, α = 91.263(14)°, β = 102.559(6)°, γ= 106.339(13)°, Z = 4 and R = 0.0668. Two copper(II) atoms are bridged by four α-methacry late groups, and each copper(II) atom is coordinated with a trimethyl phosphate molecule in the axial position, forming a distorted square pyramidal configuration. The symmetric center is between the two copper(II) atoms, and the Cu-Cu bond distance is 0.26098(6) nm. The Cu-Cu distance and magnetic studies suggest that there exist anti-ferromagnetic interactions between the two copper(II) atoms.

Kinetics and mechanism of the displacement of CO from Co4(CO)12 by phosphite ligands

Detailed kinetic data are reported for the monosubstitutions of Co4(CO)12 with phosphite ligands: P(OMe)2Ph, P(OMe)Ph2, P(OPr-i)3 and P(OPh)3, studied by conventional methods in CHCl3 as solvent. The reaction rates suggest parallel pathways of dissociation (k1) and association (k2) and show predominantly an association pathway, the low values of ΔH‡ and negative ΔS‡ adding further support to the proposed mechanism. It is also confirmed that the reaction rates are retarded due to hydrogen-bonding between the H atom of CHC13 and the O atoms of the ligands [J. Wang et al., J. Coord. Chem., 23, 345 (1991)]. The results of the reactions of Co4(CO)12 with P(OMe)3, P(OMe)2Ph and P(OMe)Ph2 in this paper suggest that no quantitative relation exists between the O atoms in the ligand and the reaction rate.

Kinetics and mechanism of CO substitution of [η5-CpFe(CO)3]PF6 with PPh3 in the presence of substituted pyridine N-oxide

Abstract The kinetics of substitution reactions of [ η -CpFe(CO) 3 ]PF 6 with PPh 3 in the presence of R-PyOs have been studied. For all the R-PyOs (R = 4-OMe, 4-Me, 3,4-(CH) 4 , 4-Ph, 3-Me, 2,3-(CH) 4 , 2,6-Me 2 , 2-Me), the reactions yeild the same product [ η 5 -CpFe(CO) 2 PPh 3 ]PF 6 , according to a second-order rate law that is first order in concentrations of [ η 5 -CpFe(CO) 3 ]PF 6 and of R-PyO but zero order in PPh 3 concentration. These results, along with the dependence of the reaction rate on the nature of R-PyO, are consistent with an associative mechanism. Activation parameters further support the bimmolecular nature of the reactions: ΔH ≠ = 13.4 ± 0.4 kcal mol −1 , ΔS ≠ = −19.1 ± 1.3 cal k −1 mol −1 for 4-PhPyO; ΔH ≠ = 12.3 ± 0.3 kcal mol −1 , ΔS ≠ = 24.7 ±1.0 cal K −1 mol −1 for 2-MePyO. For the various substituted pyridine N -oxides studied in this paper, the rates of reaction increase with the increasing electron-donating abilities of the substituents on the pyridine ring or N -oxide basicities, but decrease with increasing 17 O chemical shifts of the N -oxides. Electronic and steric factors contributing to the reactivity of pyridine N -oxides have been quantitatively assessed.